At first, thank you for your great work!
I also don't know. The only reason for stock for me were bugs of CM9 we are proud to beat now)
Well at least there is one really annoying bug in cm9 which also appears in the stock rom though in cm9 it causes a freezes and in the stock it causes lags.
I'm talking about a bug with the wifi.
If you turn on the wifi while any app is opened (even in the background) it may happen that the wifi bug appears.
In the stock, the phone starts to lag and sometimes you get even told that no wifi can't be found even if you're standing right next to your wifi.
So now you are in a lag mode where everything seems to react much slower than normal.
Anyway you can solve this problem if you navigate yourself to the app manager in the 'lag mode' and then close all active apps.
After this, the phone connects to the wifi and everything works fine again.
If this bug appear in cm9 your phone will freeze and then restart itself.
At least i found a cheap solution for that problem by getting a widget that closes all apps by one click.
so if you activate this thing before you turn on the wifi, everything works just fine but that kind of solution doesn't really solve the main problem i think
This is at least one of the reasons why i used the stock rom a long time until i figured out how to go around the bug...